The present invention relates to a liquid crystal display (LCD) using a segmented back-to-back diode.
As known in the art, an LCD comprises a pair of transparent substrates disposed parallel to each other. A first substrate has a plurality of transparent electrodes, which define picture elements (pixels) with address lines disposed therebetween. Address lines, which also serve as the second substrate electrode, are disposed perpendicular to the address lines of the first substrate. Between the two substrates is an aligning layer (such as a polyimide), a liquid crystal, and another aligning layer. When selected address lines on both substrates have the proper voltage applied thereto, the intersection of transparent electrodes of one substrate with respect to that of the other substrate determines which pixel or pixels are turned ON.
U.S. patent application No. 671,315, filed Nov. 8, 1984, under common assignment herewith, discloses a back-to-back diode having a positive and a negative threshold voltage, for use with an LCD such as the LCD shown in U.S. Pat. No. 3,499,702. Each diode is respectively coupled in series with a pixel of the LCD in order to avoid turning ON (or partially turning ON) non-selected pixels when a active multiplexed AC drive voltage is used. Further, concurrently filed application U.S. patent application No. 728,587, filed Apr. 29, 1985, entitled "Simplified Semiconductor Back-to-Back Diode Structure and Method for Making Same", filed in the name of the present inventors, discloses an improved back-to-back diode. In particular, the diode comprises two segments so that the number of mask levels required during fabrications is reduced. This increases the yield and hence reduces the cost.
In an LCD one segment of the improved diode could be disposed on the address line, while the remaining segment could be disposed on the electrode. However due to tolerance variations in forming the diode, the effective diode area could vary causing variations in the diode current versus voltage characteristics.